The most mature and widely accepted presence detection technology is based on passive infrared (PIR) detection from human beings. These sensors are relatively low cost but are at the same time vulnerable for false triggers. False triggers may be false positive and false negative. False positive is when the sensor is triggered when nobody is present and false negative is when the sensor does not detect when somebody is present. A typical PIR sensor consists of lens to focus infrared (IR) energy onto the sensor element and control electronics to make decision on the presence detection/absence detection. FIG. 1 shows a multi-sensor system with multiple lens systems. The multiple sensors cover different sectors and increase the detection range and sensitivity. In those multi-element sensors, when one element is triggered by presence of a human being, the sensor outputs a trigger signal which in turn switches on a light source.
A false positive trigger scenario is shown in FIG. 2. A nearby object, e.g. a tree is moved by some means, e.g. by the wind. The sensor detects IR movement and may perform a false positive trigger signal. The false trigger signal in this case is generated by a difference in foreground and background, where the tree is the foreground and, e.g., a street or a building is the background. If the tree moves, different parts of the background will be sensed which can lead to a false positive trigger signal.
The false positive trigger scenarios shown in FIG. 2 are typically depending on the weather, and the environment or more precisely the contrast in background. These false positive triggers are difficult to predict and usually occur during longer periods at the same location.
False triggers of PIR-sensors will switch on lighting and/or other equipment consuming energy, which is both expensive and detrimental to the environment.
There is thus a need to provide a more robust PIR sensor that will not give false positive trigger signals from unintended objects within a PIR sector of a PIR sensor having multiple sensors. This should be achieved without adding too much cost to the sensor, since the PIR-sensors market is price sensitive due to the vast and increasing number of PIR sensors used in society.